The allegations have strained relations between Sanchez’s leftist minority coalition government and the Catalan separatist party ERC, whose support he needs to pass legislation.
Canada’s Citizen Lab group said last week that more than 60 people linked to the Catalan separatist movement had been targets of Pegasus spyware after a failed independence bid in 2017.
Elected officials, including current and former Catalan regional leaders, were among those targeted by the spyware made by Israel’s NSO group, which infiltrates mobile phones to extract data or activate a camera or microphone and spy on its owners.
“We will be accountable,” Sánchez said during a parliamentary debate, his first public comments on the spying allegations.
“This is a serious issue which demands serious answers,” he added.
The government said Sunday it would launch inquiries into the affair.
It has neither confirmed nor denied whether it uses Pegasus or similar spyware, saying only that any surveillance was carried out under the supervision of judges.
Sanchez vowed “maximum transparency”, saying documents could be declassified to help the investigations.
At the same time, he defended Spain’s intelligence service, the CNI, saying everything it had done had been carried out “scrupulously and with rigour, within the framework of the law”.
Citizen Lab, which operates out of the University of Toronto, focuses on high-tech human rights abuses.
In its analysis it said it could not directly attribute the spying operations to the government, but that circumstantial evidence pointed to Spanish authorities.
Those targeted included “members of the European Parliament, Catalan Presidents, legislators, jurists, and members of civil society organisations”, it said.
Catalan separatists have pointed the finger at Spain’s intelligence service.
Top-selling Spanish daily El Pais reported Tuesday that the service had court approval to spy on Catalan separatist figures, and that the spying targeted far fewer people than alleged by Citizen Lab.
Catalonia, in northeast Spain, has been for several years at the centre of a political crisis between separatists, who control the executive and the regional parliament, and the central government in Madrid.
Tensions had eased since dialogue began between Sánchez’s government and the regional authorities in 2020 and the granting of pardons to nine pro-independence leaders last year.